Looper: Drop default parameters in favor of a safer overload.

The idea is that if you're writing code that wants fd/events/data on
return from pollOnce() / pollAll() you should really pass in all of those
arguments.  When I changed the Looper API earlier, it was difficult
to ensure that all callers were passing the right parameters since they
were relying on default parameters to some degree so usage mistakes
would not have been caught by the compiler.

Change-Id: I1f2812894270aaf1515017ac1616b6b312d9b565